A detailed map of optical linear polarization measured at 3000 points in the Orion nebula is presented which covers about 8 arcmin centered between Theta-1 and Theta-2 Ori. A centrosymmetric polarization pattern is observed to the north, west, and south of the Trapezium, with the E-vectors mainly normal to the radius vector from that formation to the point of observation. This effect is attributed to the scattering of light from the Trapezium by nebular material. It is found that the pattern in the region around Theta-2 Ori tends to center on that star, suggesting that this area of the nebula is mainly illuminated by Theta-2 Ori. The hypothesis that small condensations near Theta-2 Ori are illuminated by that star is shown to be supported by the polarization pattern in this area. Polarization around the 'bar' and the Kleinmann-Low infrared nebula is discussed, and problems in explaining the observed degree of polarization are considered.